lecture 20- groundwater

groundwater

liquid water that resides in porous space of sediment or rock under the surface of the earth

hydrogeology

study of groundwater

porosity

total volume of open space is termed porosity; different rocks have different porosities

permeability

the ease of fluid flow through geologic materials due to pore size and interconnectedness of pores. varies significantly in geologic materials, much more than most other physical properties

aquifer

a high porosity, high permeability rock that transmits water easily

aquitard

a low permeability rock that hinders water flow

unconfined aquifer

lies at the surface, easily contaminated and is recharged directly by rainfall or surface water.

confined aquifer

lies beneath an aquitard, isolated from surface and less likely to be contaminated

water table

water surface defining the top of of an unconfined aquifer

what does a water table separate

the unsaturated zone from the saturated zone

what is the capillary fringe

forms at the boundary and is the transition zone between the unsaturated and saturated zones

what causes depth of water table to vary

climate and the seasons, humid regions have gaining stream (receive groundwater), dry regions losing streams (lose water)

Hydraulic head

the level to which water rises in a drilhole, essentially the water pressure or elevation

hydraulic gradient

difference in head at two different locations divided by the distance of length of the flow path between them

darcy’s law

states that groundwater flow=HG*permeability

springs

discrete locations of natural groundwater discharge

caves and karst landscapes develop when

weakly acidic groundwater dissolves limestone. CO2 is added to rainwater as it falls throuhg the air and to groundwater from decaying organic matter in the soil. CO2 reacts with water to form carbonic acid

Joints

conduits for water, dissolved by flow, creating a network of caves and passageways

karst landscapes

formed through limestone dissolution, common elements include disappearing streams, natural bridges, caves, speleothems, sinkholes, and springs

sinkhole

a large hole in the ground formed by dissolution of rock or collapse of. a cave

recharge zone

the area where water enters the aquifer

artesian wells

free-flowing hills tapping confined aquifers

cone of depression

develops around the well

drawdown

term used for the drop in water level

groundwater problems

threatened by mismanagement, overuse, and pollution